How to add back buttons to admin panel

The company I do social media for has had me make tweaks to their website - most have been fairly easy code or editing fixes, but my most annoying issue at the moment is how to remove dead footer links. In trying to troubleshoot I also realized that I am missing a lot of the other buttons and features in the side panel when you are on the admin page. I am not sure if this is because of the previous company that set up their webpage, who removed possible buttons in the process - if that’s possible? My admin panel is missing most of the buttons you would see on a “normal” admin panel, seen below:

admin panel I found from a discussion board:

Especially - I can’t find the “Customizer” to update my footer links (I think that is where I shoud start to remove links?) - I’ve read multiple different forums and nothing has addressed my issue. Any and all help is much appreciated. Thanks!